The present invention relates to the field of surgical apparatus and more specifically, to retractors used in surgery.
Retractors of all shapes and sizes have been present since the dawn of surgery. A common type of retractor is the chest retractor or thoracic retractor. Retractors of this category may comprise sternum retractors, thoracotomy retractors, mini-thoracotomy retractors, mini-sternotomy retractors, and retractors used for the surgical harvesting of internal thoracic arteries through a sternotomy or intercostal approach incision. For instance, such internal thoracic arteries may comprise the left internal mammary artery.
Sternum retractors are commonly used in cardiac surgery. Cardiac surgery may take several forms. For instance, these forms include traditional coronary artery bypass graft surgery (CABG) requiring the heart-lung machine, CABG surgery performed directly on a beating heart, minimally invasive direct coronary artery bypass surgery (MIDCAB), heart valve repair surgery, heart valve replacement surgery and surgery to correct a septal wall defect, whether atrial or ventricular. Thoracic retractors serve to incise, penetrate and retract the thoracic structure, namely the surface, underlying tissue and bone structure of a patient, in order to access the body organs and internal body tissue contained within the patient""s thorax. In the case of a sternum retractor, the thoracic structure in question is the patient""s sternum and entire ribcage. The body organs and internal body tissue exposed by use of a sternum retractor will comprise the coronary organs, which include in particular the heart, the heart""s arteries and veins, the surrounding tissue and vessels, the pericardium, the thymus, the pleura, and any other tissue within the mediastinum or the space between the two lungs. Sternum retractors are typically used in CABG surgeries or valve replacement surgeries.
The drive in recent years for less invasive cardiac surgery has resulted in smaller chest incisions and consequently smaller chest retractors as well. In minimally invasive cardiac surgery, such as MIDCAB, mini-thoracotomy retractors were introduced to laterally retract a pair of adjacent ribs and expose the underlying coronary organs through the resultant intercostal space.
Most known chest retractors have an elongate rack bar and two retracting arms, namely a fixed retracting arm and a movable retracting arm. Both arms typically extend in a direction substantially normal to the rack bar. The movable arm can be displaced along the rack bar using a crank, which also acts as a torque lever, to activate a pinion mechanism. Two blades are provided, usually below the retractor arms, to interface with the patient""s sternum or skin, and which forms part of the thoracic structure. The basic design and mechanism for separating the two or more spreader members or retractor arms of chest retractors have remained relatively unchanged since the first introduction of retractors in cardiac surgery. Consequently, cardiac surgeons have developed a manual proficiency in using the current retractors.
In all chest retractors, there is a resistance to retraction by the patient""s thoracic structure and by the retractor itself, which the surgeon must overcome in deploying the retractor to expose the coronary organs. The separating force the surgeon applies is mainly a function of the geometry of the rack and pinion mechanism, the length of the retractor arm, and the friction at the interface between all moving components in the retractor assembly. The separating force to overcome the resistance load on the retractor may at times be excessive since:
a patient may be very corpulent;
a patient""s bones may be very brittle, and therefore especially resistant to rotation of the ribs about the spine;
the retractor blade design may result in concentrated loads being generated at locations remote from the rack bar and pinion mechanism;
friction in the retractor system may be high; and
wear may have occurred at the mechanical interface between moving components.
The deployment of the retractor, and more specifically the relative movement of the retractor arms, may at times be intermittent, or xe2x80x9cjerkyxe2x80x9d and not smooth, since:
the thoracic structure generally imposes variable loads on the retractor as a function of its retracted opening;
the meshing of the crank and pinion mechanism of the retractor may not be continuous, such that the load at the crank handle may vary as a function of the pinion position within the rack grooves and consequently as a function of the circumferential orientation of crank handle;
the load to overcome friction between retractor components to set retraction in motion is typically higher than the load to keep said components in motion;
friction between moving retractor components may be subject to variation given uneven wear in components; and
the friction forces associated with the operation of the retractor are normally linked to the resistance force exerted by the thoracic structure, which is itself variable as a function of its retracted opening.
In most chest retractors, the pinion mechanism usually consists of two pins which engage the rack teeth within grooves formed therebetween in a variety of orientations depending on the rotation of the pinion assembly (and the crank handle usually attached to the pinion assembly). This results in a substantially stable orientation when both pins are engaged with the rack teeth, and a substantially unstable orientation when only one pin is engaged with a rack tooth. This also results in an alternation of discrete and substantially stable locked positions with unstable unlocked positions of the retractor arms along the entire length of the rack.
Based on the foregoing, it would therefore be advantageous to provide a surgical retractor, for instance a sternum retractor, with easier deployment in cardiac surgery.
Thus, it is one object of the present invention to attempt to reduce the separating force and torque the surgeon must apply to the retractor, to effect retraction in surgery.
It is a further object of the present invention to seek to maintain more uniform separating loads by normalizing the variables in chest retractor design discussed above and experienced during deployment in surgery.
It is a further object of the present invention to aim to reduce the risk of injury to a patient by providing improvements to retractors, for instance sternum retractors, that allow the surgeon to deploy said retractors in a controlled manner free from sudden or intermittent movements.
It is a further object of the present invention to provide a chest retractor, for instance a sternum retractor, which may more readily be cleaned and sterilized.
It is a further object of the invention to provide a retractor design which is intended to reduce concentrated loads sometimes found at the extremities of a surgical incision, when compared to certain prior art retractors, and for a given retracted opening in the thoracic structure when measured at the mid length location along the incision.
It is a further object of the present invention to provide a chest retractor with contoured retractor blades adapted to more closely conform to the ribcage halves along a sternotomy incision as the thoracic structure is retracted.
It is an additional object of the present invention to provide a retractor having a continuous variable range of lockable open retracted positions.
It is an additional object of the present invention to retrofit existing retractors, for instance sternum retractors, with improvements that aim to reduce and normalize separating loads which the surgeon must apply during retraction of the thoracic structure therewith.
It is an additional object of the present invention to apply the concepts and principles of this invention, as they relate to chest retractors and more specifically to sternum retractors, to other types of retractors.
These and other objects of the present invention will become apparent from the description of the present invention and its preferred embodiments which follows.
According to one broad aspect of the present invention, there is provided a surgical retractor having an elongate guide member, and having first and second spreader arms each extending substantially transversely of the guide member and each extending therefrom generally in the same direction, the first and second spreader arms being disposed generally parallel to each other, the first spreader arm being movable along the length of the guide member from a first position, wherein the spreader arms are adjacent one another, to a second position, wherein the spreader arms are spaced apart from one another, to thereby effect retraction of a surgical incision; characterized in that the surgical retractor comprises: an actuator for effecting said movement of the first spreader arm, the actuator being operatively connected to the guide member and to the first spreader arm, and wherein the actuator is translatable along the length of the guide member; and a low friction interfacing member, the low friction interfacing member being disposed between the actuator and the guide member at a point of contact of said actuator with said guide member.
With reference to preferred embodiments of the invention, the low friction interfacing member may advantageously be connected either to a pinion mechanism housing or be inserted in a slider slot provided along the length of a corresponding rack bar. The low friction interfacing member is preferably of an open configuration which tends to facilitate sterilization and easy cleaning of blood products from constituent elements prior to sterilization. As well, the low friction interfacing member is preferably non-lubricated tending to ensure inert and sterile environment during surgery.
The thoracic retractor may also advantageously provided with a pinion arrangement having a friction reducing member. As well, the driving member therefor may be provided with a friction reducing member such as a bearing.
The retractor may also comprise a locking arrangement to allow the adaptor to be secured at any longitudinal position along the rack bar, independently of the pinion""s position.
A low friction interfacing member according to the present invention may also be used as a retrofit arrangement for existing retractors.
The pinion arrangement preferably comprises two pinions, but those skilled in this art will appreciate that more pinions may also be provided.
All the foregoing features contribute to attempt to optimize the operation and safety of the retractor.
The retractor according to the present invention seeks to reduce the separating force and torque which the surgeon must apply at the driving member of the retractor and thereby tends to facilitate its deployment. As well, the retractor of the present invention attempts to substantially normalize retraction loads; that is, it is intended to allow the surgeon to sense more uniform loads and to thereby result in a steadier deployment of the retractor throughout its open range. Since a jerky deployment of the retractor can lead to sudden retraction movements, normalization may result in less risk of inadvertent tissue trauma or sternum fracture. Thus the present invention describes a low-friction interfacing member for providing load reduction and load normalization in thoracic retractors.
In surgical interventions which obtain access to the coronary organs via a midline sternotomy incision, the nature of the surgical incision is substantially linear since the sternum or breastbone is cut in two. The patient""s thoracic structure usually imposes the greatest resistance to retraction at the extremities of the surgical incision, where tearing of tissue most often occurs. This also tends to result in the highest concentration of resistance load being applied to the retractor arms at the free ends thereof, namely at the extremity of the incision location which is furthest away from the rack and pinion mechanism of the retractor. The retractor of this invention, with its arcuate spreader arms and contoured thoracic structure engaging members is expected to reduce these concentrated loads at the incision extremities for a desired retracted opening in the thoracic structure at the mid length location along the surgical incision. This would therefore be advantageous since the overall separating force the surgeon must apply will also be reduced for a given opening in the thoracic structure.
In retracting a patient""s thoracic structure subsequent to a midline sternotomy, the two halves of the ribcage do not have a tendency to spread apart in a parallel orientation along the sternotomy incision. The top portion of the ribcage tends to go from a generally cylindrical-shaped surface, when the incision is not retracted, to a generally barrel-shaped surface when the incision is retracted. That is, the center portion of the ribcage along the sternotomy incision retracts more readily in an outward and upward direction than the extremities of the incision, which are somewhat restricted by the endpoints thereof at the patient""s abdomen and collarbone. This forms a lens-shaped opening for the retracted incision. Many prior art retractors do not accommodate this barrelling behaviour. The retractor of this invention, with its contoured thoracic structure engaging members that interface with the two halves of the patient""s incised sternum and that conform closely to this non-parallel barrelling of the ribcage halves along the sternotomy incision during retraction, would offer advantages in tending to minimize the likelihood of sternal breakages and induced tissue trauma.